Error Handling & Debugging

Programming code might contain syntax errors, or logical errors. Searching for (and fixing) errors in programming code is called code debugging.

ORDER OF EXECUTION

To find the source of an error, it helps to know how scripts are processed. The order in which statements are executed can be complex; some tasks cannot complete until another statement or function has been run

in JS you always make wrong steps by mistake and theres ways that can help you to find these errors at the first how js work : its work as the concept of STACK which it’s read one line of code at atime. and when when it need any data fromany other function it stack the function on the top.and for the error If a Js statement generates an error, then it throws an exception at that point, the interpreter stops and looks for exception-handling code.

you can deal with errors by :

1. debug the script
2. handle errors by Throw and Try to Catch. The try statement lets you test a block of code for errors.
   • The catch statement lets you handle the error.

• The throw statement lets you create custom errors.

• The finally statement lets you execute code, after try and catch, regardless of the result.

Tools

JavaScript console it will tell you when there is a problem with a script, where to look for the problem, and what kind of issue it seems to be. by using console.log(); in the code and you can typing on it whatever the browser you use it and console.group()use it to write a set of related data to the console by console.groupEnd () method at the end of code.console.table () method to output a table.

You can pause the execution of a script on any line using breakpoints by click on line number you want in source option to stop on and when you run it will stop and You can indicate that a breakpoint should be triggered if a condition that you specify is met by Right-click on a line number,Select Add Conditional Breakpoint,then enter a condition into the popup box. If you know something might cause a problem for your script, you can generate your own errors before the interpreter creates them using throw new Error(‘message);

Major Browsers’ Debugging Tools Normally, you activate debugging in your browser with F12, and select “Console” in the debugger menu.

Otherwise follow these steps:

Chrome

Open the browser. From the menu, select “More tools”. From tools, choose “Developer tools”. Finally, select Console.

Firefox Open the browser. From the menu, select “Web Developer”. Finally, select “Web Console”. Edge Open the browser. From the menu, select “Developer Tools”. Finally, select “Console”.

Opera Open the browser. From the menu, select “Developer”. From “Developer”, select “Developer tools”. Finally, select “Console”.

Safari Go to Safari, Preferences, Advanced in the main menu. Check “Enable Show Develop menu in menu bar”. When the new option “Develop” appears in the menu: Choose “Show Error Console”.

DEBUGGER KEYWORD

he debugger keyword stops the execution of JavaScript, and calls (if available) the debugging function.

This has the same function as setting a breakpoint in the debugger.

If no debugging is available, the debugger statement has no effect.

With the debugger turned on, this code will stop executing before it executes the third line.